The invention relates to a broadband microwave detector arrangement comprising a detector diode.
The operating frequency range of a detector arrangement in a waveguide is inherently limited (assuming operation in the dominant mode) to a band between the cut-off frequencies of the dominant mode and the next, higher-order mode.
A detector arrangement in a transmission line may be operable over a broader frequency range, particularly a range extending down to low microwave frequencies. ("Transmission line" is to be understood to be means for propagating a TEM or quasi-TEM wave).
It is generally desirable that a detector arrangement should not reflect a high proportion of incident power; it is also of course desirable that the detector diode itself should absorb a fairly high proportion of incident power and convert it to video frequencies. The impedance of a detector diode may differ greatly from the characteristic impedance of a transmission line to which it is connected, and these criteria may conflict. An arrangement which is suitable for fairly low microwave frequencies is disclosed in U.K. Patent Specification No. 1,385,111. In this arrangement, a diode having an impedance of 200-300 ohms is connected to a 50 ohms transmission line through a low-impedance capacitance and is connected in parallel with a resistance of 75 ohms. This arrangement is not, however, suitable for frequencies approaching the series resonant frequency of the detector diode; in the region of this frequency, the diode shunts the 75 ohms resistance with a low impedance, causing a severe mismatch.